Varying the Length of a Temperature Sensing Element of a Radiofrequency Probe Based on Desired Lesion Size

ABSTRACT

A method for preparing a cooled radiofrequency probe for use to treat tissue of a patient&#39;s body includes providing a plurality of cooled radiofrequency probes. Each of the plurality of cooled radiofrequency probes includes an elongate member with a distal region and a proximal region. The distal regions each have an electrically and thermally-conductive energy delivery device for delivering one of electrical and radiofrequency energy to the patient&#39;s body. The electrically and thermally-conductive energy delivery devices each have one or more internal lumens for circulating a cooling fluid therethrough and an electrically and thermally-conductive protrusion having a temperature sensing element. The temperature sensing elements of each protrusion extends from a distal end of the energy delivery device. Further, each of the temperature sensing elements has a different length that extends from the distal end of the energy delivery device. The method further includes determining at least one of a desired lesion size or a desired rate of power delivery required to treat the tissue. As such, the method includes selecting one of the probes from the plurality of cooled radiofrequency probes based on the length of the temperature sensing element thereof that achieves the desired lesion size or the desired rate of power delivery.

RELATED APPLICATIONS

The present invention claims priority to U.S. Provisional ApplicationNo. 62/677,712 filed on May 30, 2018, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to a system and method forapplying energy for the treatment of tissue, and more particularly to asystem and method that allows for varying the length of a temperaturesensing element of a cooled radiofrequency probe.

BACKGROUND

Lower back injuries and chronic joint pain are major health problemsresulting not only in debilitating conditions for the patient, but alsoin the consumption of a large proportion of funds allocated for healthcare, social assistance and disability programs. In the lower back, discabnormalities and pain may result from trauma, repetitive use in theworkplace, metabolic disorders, inherited proclivity, and/or aging. Theexistence of adjacent nerve structures and innervation of the disc arevery important issues in respect to patient treatment for back pain. Injoints, osteoarthritis is the most common form of arthritis pain andoccurs when the protective cartilage on the ends of bones wears downover time.

A minimally invasive technique of delivering high-frequency electricalcurrent has been shown to relieve localized pain in many patients.Generally, the high-frequency current used for such procedures is in theradiofrequency (RF) range, i.e. between 100 kHz and 1 GHz and morespecifically between 300-600 kHz. The RF electrical current is typicallydelivered from a generator via connected electrodes that are placed in apatient's body, in a region of tissue that contains a neural structuresuspected of transmitting pain signals to the brain. The electrodesgenerally include an insulated shaft with an exposed conductive tip todeliver the radiofrequency electrical current. Tissue resistance to thecurrent causes heating of tissue adjacent resulting in the coagulationof cells (at a temperature of approximately 45° C. for smallunmyelinated nerve structures) and the formation of a lesion thateffectively denervates the neural structure in question. Denervationrefers to a procedure whereby the ability of a neural structure totransmit signals is affected in some way and usually results in thecomplete inability of a neural structure to transmit signals, thusremoving the pain sensations. This procedure may be done in a monopolarmode where a second dispersive electrode with a large surface area isplaced on the surface of a patient's body to complete the circuit, or ina bipolar mode where a second radiofrequency electrode is placed at thetreatment site. In a bipolar procedure, the current is preferentiallyconcentrated between the two electrodes.

To extend the size of a lesion, radiofrequency treatment may be appliedin conjunction with a cooling mechanism, whereby a cooling means is usedto reduce the temperature of the electrode-tissue interface, allowing ahigher power to be applied without causing an unwanted increase in localtissue temperature that can result in tissue desiccation, charring, orsteam formation. The application of a higher power allows regions oftissue further away from the energy delivery device to reach atemperature at which a lesion can form, thus increasing the size/volumeof the lesion.

The treatment of pain using high-frequency electrical current has beenapplied successfully to various regions of patients' bodies suspected ofcontributing to chronic pain sensations. For example, with respect toback pain, which affects millions of individuals every year,high-frequency electrical treatment has been applied to several tissues,including intervertebral discs, facet joints, sacroiliac joints as wellas the vertebrae themselves (in a process known as intraosseousdenervation). In addition to creating lesions in neural structures,application of radiofrequency energy has also been used to treat tumorsthroughout the body. Further, with respect to knee pain, which alsoaffects millions of individuals every year, high-frequency electricaltreatment has been applied to several tissues, including, for example,the ligaments, muscles, tendons, and menisci.

Due to the large volume lesions generated by cooled radiofrequency probeprocedures, care must be taken when treating sensitive locations,particularly around areas that cannot sustain significant collateralablative damage. Still other anatomical locations with more nervevariability and less sensitive surrounding tissue may require largerlesions. Thus, the art is continuously seeking new and improved systemsand methods for treating chronic pain using cooled RF ablationtechniques, and more particularly to improved systems and methods thatallow for varying the length of a temperature sensing element of acooled radiofrequency probe.

SUMMARY OF THE INVENTION

Objects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one aspect, the present invention is directed to a method forpreparing a cooled radiofrequency probe for use to treat tissue of apatient's body. The method includes providing a plurality of cooledradiofrequency probes. Each of the plurality of cooled radiofrequencyprobes includes an elongate member with a distal region and a proximalregion. The distal regions each have an electrically andthermally-conductive energy delivery device for delivering one ofelectrical and radiofrequency energy to the patient's body. Theelectrically and thermally-conductive energy delivery devices each haveone or more internal lumens for circulating a cooling fluid therethroughand an electrically and thermally-conductive protrusion having atemperature sensing element. The temperature sensing elements of eachprotrusion extends from a distal end of the energy delivery device.Further, each of the temperature sensing elements has a different lengththat extends from the distal end of the energy delivery device. Themethod further includes determining at least one of a desired lesionsize or a desired rate of power delivery required to treat the tissue.As such, the method includes selecting one of the probes from theplurality of cooled radiofrequency probes based on the length of thetemperature sensing element thereof that achieves the desired lesionsize or the desired rate of power delivery.

In one embodiment, the lesion size or volume varies with the differentlengths of the temperature sensing elements. In such embodiments,temperature sensing elements having longer lengths are configured togenerate lesions of smaller sizes, whereas temperature sensing elementshaving shorter lengths are configured to generate lesions of largersizes.

In another embodiment, the different lengths of the temperature sensingelements may be less than about 1 millimeter (mm). For example, incertain embodiments, the different lengths of the temperature sensingelements may range from about 0.20 mm to about 0.70 mm.

In further embodiments, the desired lesion size and/or the desired rateof power delivery may be based on a treatment procedure type of thetissue.

In additional embodiments, the method may include measuring thetemperature of the tissue using the selected temperature sensingelement. In certain embodiments, each of the temperature sensingelements may also have a different shape.

In yet another embodiment, the method may further include decoupling atemperature control of the temperature sensing element from the powersource within a certain operating envelope by controlling the coolingmedium flow rate in a closed loop manner.

In another aspect, the present disclosure is directed to a system fortreating tissue of a patient's body. The system includes a power sourceand a plurality of cooled radiofrequency probes communicatively coupledto the power source. Each of the probes includes an elongate member witha distal region and a proximal region. The distal regions have anelectrically and thermally-conductive energy delivery device fordelivering one of electrical and radiofrequency energy to the patient'sbody. The electrically and thermally-conductive energy delivery deviceshave one or more internal lumens for circulating a cooling fluidtherethrough and an electrically and thermally-conductive protrusionhaving a temperature sensing element. The temperature sensing elementsextend from a distal end of the energy delivery device. Each of thetemperature sensing elements has a different length that extends fromthe distal end of the energy delivery device. Thus, a user can selectone of the probes from the plurality of cooled radiofrequency probesbased on the length of the temperature sensing element thereof thatachieves a desired lesion size or a desired rate of power delivery. Itshould also be understood that the system may further include any of theadditional features as described herein.

In yet another aspect, the present disclosure is directed to a method oftreating tissue of a patient's body. The method includes providing aplurality of cooled radiofrequency probes. Each of the plurality ofcooled radiofrequency probes includes an elongate member with a distalregion and a proximal region. The distal regions each have anelectrically and thermally-conductive energy delivery device fordelivering one of electrical and radiofrequency energy to the patient'sbody. The electrically and thermally-conductive energy delivery deviceseach have one or more internal lumens for circulating a cooling fluidtherethrough and an electrically and thermally-conductive protrusionhaving a temperature sensing element. The temperature sensing elementseach extend from a distal end of the energy delivery device. Further,each of the temperature sensing elements has a different length thatextends from the distal end of the energy delivery device. The methodfurther includes determining at least one of a desired lesion size or adesired rate of power delivery required to treat the tissue. As such,the method includes selecting one of the probes from the plurality ofcooled radiofrequency probes based on the length of the temperaturesensing element thereof that achieves the desired lesion size or thedesired rate of power delivery. Further, the method includes insertingthe selected probe into the patient's body and routing the selectedprobe to the tissue of the patient's body. Moreover, the method includessimultaneously circulating the cooling fluid through the one or moreinternal lumens via at least one pump assembly and delivering energyfrom the power source to the tissue through the energy delivery device.It should also be understood that the method may further include any ofthe additional features and/or steps as described herein.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 illustrates a portion of one embodiment of a system for applyingradiofrequency electrical energy to a patient's body according to thepresent disclosure;

FIG. 2 illustrates an isometric view of one embodiment of the handle ofthe probe assembly according to the present disclosure;

FIG. 3 illustrates a longitudinal cross-section of one embodiment of ahandle of the probe assembly according to the present disclosure;

FIG. 4 illustrates a perspective cut-away view of one embodiment of adistal tip region of a probe assembly according to the presentdisclosure;

FIG. 5 illustrates detailed, side view of the temperature sensingelement of the probe assembly according to the present disclosure;

FIG. 6 illustrates side views of a plurality of temperature sensingelements of different probes according to the present disclosure,particularly illustrates temperature sensing elements each having adifferent length that extends from the distal end of the energy deliverydevice;

FIG. 7 illustrates an axial cross-sectional view through the distal tipregion of the probe assembly shown in FIG. 4 along line 7-7;

FIG. 8 illustrates an axial cross-sectional view through a more proximalportion of the distal tip region of the probe assembly shown in FIG. 4along line 8-8;

FIG. 9 illustrates two probes placed within an intervertebral discaccording to the present disclosure;

FIG. 10 illustrates a perspective view of one embodiment of a pumpassembly according to the present disclosure;

FIG. 11 illustrates a block diagram of one embodiment of a pump assemblyaccording to the present disclosure;

FIG. 12 illustrates a flow diagram of one embodiment of a method oftreating tissue of a patient's body according to the present disclosure;

FIG. 13 illustrates a block diagram of one embodiment of a treatmentprocedure for actively controlling energy delivered to tissue in thepatient's body by controlling an amount of energy delivered by theenergy delivery devices and a flow rate of the pumps of the pumpassembly according to the present disclosure;

FIG. 14 illustrates graphs of power (y-axis) versus time (x-axis) andtemperature (y-axis) versus time (x-axis), respectively, for the sametest procedure according to the present disclosure;

FIG. 15 illustrates graphs of impedance (y-axis) versus time (x-axis),temperature (y-axis) versus time (x-axis), and power (y-axis) versustime (x-axis), respectively, for three treatment procedures that eachutilize an internally-cooled probe assembly with inherently high-powerdemand and manual feedback control, when no impedance mitigation isimplemented according to conventional construction;

FIG. 16 illustrates graphs of impedance (y-axis) versus time (x-axis),temperature (y-axis) versus time (x-axis), and power (y-axis) versustime (x-axis), respectively, for three treatment procedures that eachutilize an internally-cooled probe assembly with pump-modulated powercontrol and impedance mitigation are implemented according to thepresent disclosure,

FIG. 17 illustrates one embodiment of a graph of energy (y-axis) versuslesion area (x-axis) to depict various advantages according to thepresent disclosure,

FIG. 18 illustrates another embodiment of a graph of energy (y-axis)versus lesion area (x-axis) to depict various advantages according tothe present disclosure,

FIG. 19 illustrates one embodiment of a graph of energy (y-axis) versusthermocouple protrusion length (x-axis) to depict various advantagesaccording to the present disclosure, and

FIG. 20 illustrates one embodiment of a graph of lesion size (y-axis)versus thermocouple protrusion length (x-axis) to depict variousadvantages according to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to one or more embodiments of theinvention, examples of the invention, examples of which are illustratedin the drawings. Each example and embodiment is provided by way ofexplanation of the invention, and is not meant as a limitation of theinvention. For example, features illustrated or described as part of oneembodiment may be used with another embodiment to yield still a furtherembodiment. It is intended that the invention include these and othermodifications and variations as coming within the scope and spirit ofthe invention.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

For the purposes of this invention, a lesion refers to the region oftissue that has been irreversibly damaged as a result of the applicationof thermal energy, and the invention is not intended to be limited inthis regard. Furthermore, for the purposes of this description, proximalgenerally indicates that portion of a device or system next to or nearerto a user (when the device is in use), while the term distal generallyindicates a portion further away from the user (when the device is inuse).

Referring now to the drawings, FIG. 1 illustrates a schematic diagram ofone embodiment of a system 100 of the present invention. As shown, thesystem 100 includes a generator 102, a cable 104, first, second, third,and fourth probe assemblies 106 (only one probe assembly is shown), oneor more cooling devices 108, a pump cable 110, one or more proximalcooling supply tubes 112 and one or more proximal cooling return tubes114. As shown in the illustrated embodiment, the generator 102 is aradiofrequency (RF) generator, but may optionally be any power sourcethat may deliver other forms of energy, including but not limited tomicrowave energy, thermal energy, ultrasound and optical energy.Further, the generator 102 may include a display incorporated therein.The display may be operable to display various aspects of a treatmentprocedure, including but not limited to any parameters that are relevantto a treatment procedure, such as temperature, impedance, etc. anderrors or warnings related to a treatment procedure. If no display isincorporated into the generator 102, the generator 102 may include meansof transmitting a signal to an external display. In one embodiment, thegenerator 102 is operable to communicate with one more devices, forexample with one or more of first and second probe assemblies 106 andthe one or more cooling devices 108. Such communication may beunidirectional or bidirectional depending on the devices used and theprocedure performed.

In addition, as shown, a distal region 124 of the cable 104 may includea splitter 130 that divides the cable 104 into two or more distal ends136 such that the probe assemblies 106 can be connected thereto. Aproximal end 128 of the cable 104 is connected to the generator 102.This connection can be permanent, whereby, for example, the proximal end128 of the cable 104 is embedded within the generator 102, or temporary,whereby, for example, the proximal end 128 of cable 104 is connected togenerator 102 via an electrical connector. The two or more distal ends136 of the cable 104 terminate in connectors 140 operable to couple tothe probe assemblies 106 and establish an electrical connection betweenthe probe assemblies 106 and the generator 102. In alternateembodiments, the system 100 may include a separate cable for each probeassembly 106 being used to couple the probe assemblies 106 to thegenerator 102. Alternatively, the splitter 130 may include more than twodistal ends. Such a connector is useful in embodiments having more thantwo devices connected to the generator 102, for example, if more thantwo probe assemblies are being used.

The cooling device(s) 108 may include any means of reducing atemperature of material located at and proximate to one or more of theprobe assemblies 106. For example, as shown in FIG. 10, the coolingdevices 108 may include a pump assembly 120 having one or moreperistaltic pumps 122 operable to circulate a fluid from the coolingdevices 108 through one or more proximal cooling supply tubes 112, theprobe assemblies 106, one or more proximal cooling return tubes 114 andback to the one or more cooling devices 108. For example, as shown inthe illustrated embodiment of FIGS. 10 and 11, the pump assembly 120includes four peristaltic pumps 122 coupled to a power supply 126. Insuch embodiments, as shown in FIG. 11, each of the plurality of pumps122 may be in separate fluid communication with one of the probeassemblies. The fluid may be water or any other suitable fluid or gas.In alternate embodiments, the pump assembly 120 may include only oneperistaltic pump or greater than four pumps. In addition, as shown inFIG. 11, each of the pumps 122 may have an independent speed (i.e. RPM)controller 125 that is configured to independent adjust the speed of itsrespective pump.

Still referring to FIG. 1, the system 100 may include a controller forfacilitating communication between the cooling devices 108 and thegenerator 102. In this way, feedback control is established between thecooling devices 108 and the generator 102. The feedback control mayinclude the generator 102, the probe assemblies 106 and the coolingdevices 108, although any feedback between any two devices is within thescope of the present invention. The feedback control may be implemented,for example, in a control module which may be a component of thegenerator 102. In such embodiments, the generator 102 is operable tocommunicate bi-directionally with the probe assemblies 106 as well aswith the cooling devices 108. In the context of this invention,bi-directional communication refers to the capability of a device toboth receive a signal from and send a signal to another device.

As an example, the generator 102 may receive temperature measurementsfrom one or both of the first and second probe assemblies 106. Based onthe temperature measurements, the generator 102 may perform some action,such as modulating the power that is sent to the probe assemblies 106.Thus, both probe assemblies 106 may be individually controlled based ontheir respective temperature measurements. For example, power to each ofthe probe assemblies 106 can be increased when a temperature measurementis low or decreased when a measurement is high. This variation of powermay be different for each probe assembly. In some cases, the generator102 may terminate power to one or more probe assemblies 106. Thus, thegenerator 102 may receive a signal (e.g. temperature measurement) fromone or both of the first and second probe assemblies 106, determine theappropriate action, and send a signal (e.g. decreased or increasedpower) back to one or both of the probe assemblies 106. Alternatively,the generator 102 may send a signal to the cooling devices 108 to eitherincrease or decrease the flow rate or degree of cooling being suppliedto one or both of the first and second probe assemblies 106.

More specifically, the pumps may communicate a fluid flow rate to thegenerator 102 and may receive communications from the generator 102instructing the pumps to modulate this flow rate. In some instances, theperistaltic pumps may respond to the generator 102 by changing the flowrate or turning off for a period of time. With the cooling devices 108turned off, any temperature sensing elements associated with the probeassemblies 106 would not be affected by the cooling fluid allowing amore precise determination of the surrounding tissue temperature to bemade. In addition, when using more than one probe assembly 106, theaverage temperature or a maximum temperature in the temperature sensingelements associated with probe assemblies 106 may be used to modulatecooling.

In other embodiments, the cooling devices 108 may reduce the rate ofcooling or disengage depending on the distance between the probeassemblies 106. For example, when the distance is small enough such thata sufficient current density exists in the region to achieve a desiredtemperature, little or no cooling may be required. In such anembodiment, energy is preferentially concentrated between first andsecond energy delivery devices 192 through a region of tissue to betreated, thereby creating a strip lesion. A strip lesion ischaracterized by an oblong volume of heated tissue that is formed whenan active electrode is in close proximity to a return electrode ofsimilar dimensions. This occurs because at a given power, the currentdensity is preferentially concentrated between the electrodes and a risein temperature results from current density.

The cooling devices 108 may also communicate with the generator 102 toalert the generator 102 to one or more possible errors and/or anomaliesassociated with the cooling devices 108. For example, if cooling flow isimpeded or if a lid of one or more of the cooling devices 108 is opened.The generator 102 may then act on the error signal by at least one ofalerting a user, aborting the procedure, and modifying an action.

Still referring to FIG. 1, the proximal cooling supply tubes 112 mayinclude proximal supply tube connectors 116 at the distal ends of theone or more proximal cooling supply tubes 112. Additionally, theproximal cooling return tubes 114 may include proximal return tubeconnectors 118 at the distal ends of the one or more proximal coolingreturn tubes 114. In one embodiment, the proximal supply tube connectors116 are female luer-lock type connectors and the proximal return tubeconnectors 118 are male luer-lock type connectors although otherconnector types are intended to be within the scope of the presentinvention.

In addition, as shown in FIGS. 1 and 2, the probe assembly 106 mayinclude a proximal region 160, a handle 180, a hollow elongate shaft184, and a distal tip region 190 that includes the one or more energydelivery devices 192. Further, as shown, the proximal region 160includes a distal cooling supply tube 162, a distal supply tubeconnector 166, a distal cooling return tube 164, a distal return tubeconnector 168, a probe assembly cable 170, and a probe cable connector172. In such embodiments, the distal cooling supply tube 162 and distalcooling return tube 164 are flexible to allow for greatermaneuverability of the probe assemblies 106, but alternate embodimentswith rigid tubes are possible.

Further, in several embodiments, the distal supply tube connector 166may be a male luer-lock type connector and the distal return tubeconnector 168 may be a female luer-lock type connector. Thus, theproximal supply tube connector 116 may be operable to interlock with thedistal supply tube connector 166 and the proximal return tube connector118 may be operable to interlock with the distal return tube connector168.

The probe cable connector 172 may be located at a proximal end of theprobe assembly cable 170 and may be operable to reversibly couple to oneof the connectors 140, thus establishing an electrical connectionbetween the generator 102 and the probe assembly 106. The probe assemblycable 170 may include one or more conductors depending on the specificconfiguration of the probe assembly 106. For example, in one embodiment,the probe assembly cable 170 may include five conductors allowing probeassembly cable 170 to transmit RF current from the generator 102 to theone or more energy delivery devices 192 as well as to connect multipletemperature sensing elements to the generator 102 as discussed below.

The energy delivery devices 192 may include any means of deliveringenergy to a region of tissue adjacent to the distal tip region 190. Forexample, the energy delivery devices 192 may include an ultrasonicdevice, an electrode or any other energy delivery means and theinvention is not limited in this regard. Similarly, energy delivered viathe energy delivery devices 192 may take several forms including but notlimited to thermal energy, ultrasonic energy, radiofrequency energy,microwave energy or any other form of energy. For example, in oneembodiment, the energy delivery devices 192 may include an electrode.The active region of the electrode may be 2 to 20 millimeters (mm) inlength and energy delivered by the electrode is electrical energy in theform of current in the RF range. The size of the active region of theelectrode can be optimized for placement within an intervertebral disc,however, different sizes of active regions, all of which are within thescope of the present invention, may be used depending on the specificprocedure being performed. In some embodiments, feedback from thegenerator 102 may automatically adjust the exposed area of the energydelivery device 192 in response to a given measurement such as impedanceor temperature. For example, in one embodiment, the energy deliverydevices 192 may maximize energy delivered to the tissue by implementingat least one additional feedback control, such as a rising impedancevalue.

Referring now to FIG. 3, the distal cooling supply tube 162 and thedistal cooling return tube 164 may be connected to a shaft supply tube302 and a shaft return tube 304, respectively, within the handle 180,using connecting means 301 and 303. The connecting means 301, 303 can beany means of connecting two tubes including but not limited toultraviolet (UV) glue, epoxy or any other adhesive as well as frictionor compression fitting. Arrows 312 and 314 indicate the direction offlow of a cooling fluid supplied by the cooling devices 108. Morespecifically, in one embodiment, the shaft supply tube 302 and the shaftreturn tube 304 may be hypotubes made of a conductive material such asstainless steel that extend from the handle 180 through a lumen of thehollow elongate shaft 184 to distal tip region 190, as shown in FIG. 4,wherein arrow 408 indicates the direction of the cooling fluid flowwithin a lumen 450 defined by the energy delivery devices 192. Thenumber of hypotubes used for supplying cooling fluid and the number usedfor returning cooling fluid and the combination thereof may vary and allsuch combinations are intended to be within the scope of the presentinvention.

Referring still to FIG. 3, the handle 180 may be at least partiallyfilled with a filling agent 320 to lend more strength and stability tohandle 180 as well as to hold the various cables, tubes and wires inplace. The filling agent 320 may be epoxy or any other suitablematerial. In addition, the handle 180 may be operable to easily andsecurely couple to an optional introducer tube (discussed below) in oneembodiment where an introducer tube would facilitate insertion of theone or more probe assemblies 106 into a patient's body. For example, asshown, the handle 180 may taper at its distal end to accomplish thisfunction, i.e. to enable it to securely couple to an optional introducertube.

In one embodiment, the elongate shaft 184 may be manufactured out ofpolyimide sheath and a stainless steel tubular interior, which providesexceptional electrical insulation while maintaining sufficientflexibility and compactness. In alternate embodiments, the elongateshaft 184 may be any other material imparting similar qualities. Instill other embodiments, the elongate shaft 184 may be manufactured froman electrically conductive material and may be covered by an insulatingmaterial so that delivered energy remains concentrated at the energydelivery device 192 of the distal tip region 190. In one embodiment, theprobe assembly 106 may also include a marker 384 at some point along thehandle 180 or along the length of the elongate hollow shaft 184. In suchembodiments, the marker 384 may be a visual depth marker that functionsto indicate when the distal tip of the probe assembly 106 is located ata distal end of the introducer tube by aligning with a hub of theintroducer tube. The marker 384 will thus provide a visual indication asto the location of the distal tip of a probe assembly 106 relative to anoptional introducer tube.

Referring in detail to FIG. 4, a perspective cut-away view of oneembodiment of the distal tip region 190 of the probe assembly 106 isillustrated. As shown, the distal tip region 190 includes one or moretemperature sensing elements 402 which are operable to measure thetemperature at and proximate to the one or more energy delivery devices192. The temperature sensing elements 402 may include one or morethermocouples, thermometers, thermistors, optical fluorescent sensors orany other means of sensing temperature. In one embodiment, thetemperature sensing elements 402 are connected to the generator 102 viaprobe assembly cable 170 and cable 104 although any means ofcommunication between the temperature sensing elements 402 and thegenerator 102, including wireless protocols, are included within thescope of the present invention. More specifically, as shown, thetemperature sensing element(s) 402 may include a thermocouple junctionmade by joining a stainless steel hypotube 406 to a constantan wire 410,wherein the constantan wire 410 is insulated by insulation 412. In thisembodiment, the junction of hypotube 406 and the constantan wire 410 ismade by laser welding, although any other means of joining two metalsmay be used. Furthermore, in this embodiment, the hypotube 406 and theconstantan wire 410 extend through a lumen of the elongate shaft 184 andconnect to the probe assembly cable 170 within the handle 180.

Further, as shown particularly in FIGS. 4-6, the temperature sensingelement 402 of each probe 106 protrudes beyond the energy deliverydevice 192. More specifically, as shown, the temperature sensing element402 may have a length 414 of less than about 1 millimeter (mm) thatextends from a distal end 194 of the energy delivery device 192. Inaddition, as shown particularly in FIG. 6, the length 414 of thetemperature sensing element 402 element may be chosen to assist increating lesions of different sizes. For example, in such embodiments, auser may select one or more probes from a plurality of probes havingdifferent lengths 414 based on, e.g. a desired lesion size and/or adesired rate of power delivery based on a treatment procedure type ofthe tissue. In particular embodiments, the different lengths of thetemperature sensing elements 402 may range from about 0.20 mm to about0.70 mm. In additional embodiments, each of the temperature sensingelements 402 may also have a different shape or volume. Thus, since anactual lesion size will vary with the different lengths 414 of thetemperature sensing elements 402, temperature sensing elements 402having longer lengths (e.g. probes (C) and (D)) are configured togenerate lesions of smaller sizes, whereas temperature sensing elements402 having shorter lengths (e.g. probes (A) and (B)) are configured togenerate lesions of larger sizes.

Accordingly, the different lengths of the temperature sensing elements402 are configured to control and optimize the size of the lesion fordifferent anatomical locations, for instance creating smaller lesions inregions adjacent to critical structures such as arteries and motornerves. Thus, the different lengths of the temperature sensing elements402 of the present disclosure provide several advantages including forexample, the ability to create custom lesion volumes for differentprocedures (i.e. the control of the lesion volume is intrinsic to themechanical design of the probe, which is independent of the generator102 and algorithms). As such, existing equipment and settings can beused. In addition, the protrusion distance can be optimized to providemaximum energy output while minimizing rising impedance and powerroll-off conditions. Moreover, the different lengths of the temperaturesensing elements 402 creates a mechanical safety mechanism to preventover-ablation in sensitive anatomical regions.

In addition, the length 414 of the temperature sensing element 402 isconfigured to increase (or decrease) a power demand of the energydelivery device 192. Further, as shown, whereby the temperature sensingelement 402 includes a stainless steel hypotube 406, the hypotube 406may be electrically conductive and may be electrically coupled to theenergy delivery device 192. Thus, in such an embodiment, whereby energymay be conducted to the protrusion and delivered from the protrusion tosurrounding tissue, the protrusion may be understood to be a componentof both temperature sensing element 402 as well as the one or moreenergy delivery devices 192. Placing the temperature sensing elements402 at this location, rather than within a lumen 450 defined by theenergy delivery device 192, is beneficial because it allows thetemperature sensing element 402 to provide a more accurate indication ofthe temperature of tissue proximate to the energy delivery device 192.This is due to the fact that, when extended beyond the energy deliverydevice 192, the temperature sensing element 402 will not be as affectedby the cooling fluid flowing within the lumen 450 as it would be were itlocated within lumen 450. Thus, in such embodiments, the probe assembly106 includes a protrusion protruding from the distal region of the probeassembly, whereby the protrusion is a component of the temperaturesensing element 402.

Referring still to FIG. 4, the probe assembly 106 may further includeone or more secondary temperature sensing elements 404 located withinthe elongate shaft 184 at some distance away from the energy deliverydevice 192, and positioned adjacent a wall of the elongate shaft 184.The secondary temperature sensing elements 404 may similarly include oneor more thermocouples, thermometers, thermistors, optical fluorescentsensors or any other means of sensing temperature. For example, asshown, the secondary temperature sensing element 404 is a thermocouplemade by joining copper and constantan thermocouple wires, designated as420 and 422 respectively. Further, in certain embodiments, the copperand constantan wires 420 and 422 may extend through a lumen of theelongate shaft 184 and may connect to the probe assembly cable 170within the handle 180.

In addition, the probe assembly 106 may further include a thermalinsulator 430 located proximate to any of the temperature sensingelements 402, 404. As such, the thermal insulator 430 may be made fromany thermally insulating material, for example silicone, and may be usedto insulate any temperature sensing element from other components of theprobe assembly 106, so that the temperature sensing element will be ableto more accurately measure the temperature of the surrounding tissue.More specifically, as shown, the thermal insulator 430 is used toinsulate the temperature sensing element 404 from cooling fluid passingthrough the shaft supply tube 302 and the shaft return tube 304.

In further embodiments, the probe assembly 106 may also include aradiopaque marker 440 incorporated somewhere along the elongate shaft184. For example, as shown, in FIG. 4, an optimal location for aradiopaque marker may be at or proximate to the distal tip region 190,adjacent the energy delivery device 192. The radiopaque markers arevisible on fluoroscopic x-ray images and can be used as visual aids whenattempting to place devices accurately within a patient's body. Thesemarkers can be made of many different materials, as long as they possesssufficient radiopacity. Suitable materials include, but are not limitedto silver, gold, platinum and other high-density metals as well asradiopaque polymeric compounds. Various methods for incorporatingradiopaque markers into or onto medical devices may be used, and thepresent invention is not limited in this regard.

Referring now to FIGS. 7 and 8, cross-sectional views of portions of thedistal tip region 190, as indicated in FIG. 4, are illustrated.Referring first to FIG. 7, three hypotubes 302, 304, and 406 arepositioned within the lumen 450 defined by the elongate shaft 184 andthe energy delivery device 192. The shaft supply tube 302 and the shaftreturn tube 304 carry cooling fluid to and from the distal end of distaltip region 190, respectively. In this embodiment, hypotube 406 is madeof a conductive material such as stainless steel and is operable totransmit energy from the probe assembly cable 170 to the energy deliverydevice 192. In addition, the hypotube 406 defines a lumen within which ameans of connecting the one or more temperature sensing elements 402 tothe probe assembly cable 170 may be located. For example, if the one ormore temperature sensing elements 402 includes a thermocouple, then aconstantan wire 410 may extend from probe assembly cable 170 to thethermocouple junction through hypotube 406 as is shown in FIG. 4.Alternatively, more than one wire may be passed through the lumen ofhypotube 406 or the lumen of hypotube 406 may be utilized for anotherpurpose.

Further, as shown, the elongate shaft 184 and the electrode 192 overlapto secure the electrode in place. In this embodiment, the lumen definedby the elongate shaft 184 and the electrode 192 at this portion of thedistal tip region 190 contains a radiopaque marker 440 made of silversolder, which fills the lumen such that any cooling fluid supplied tothe probe assembly 106, that is not located within one of the coolingtubes described earlier, is confined to the distal tip region 190 ofprobe assembly 106. Thus, in such an embodiment, the silver solder maybe referred to as a flow impeding structure since it functions torestrict the circulation of fluid to a specific portion (in this case,at least a portion of distal region 190) of the probe assembly 106. Inother words, cooling fluid may flow from the cooling devices 108,through the cooling supply tubes to the distal tip region 190 of theprobe assembly 106. The cooling fluid may then circulate within thelumen 450 defined by the electrode 192 to provide cooling thereto. Assuch, the internally-cooled probe as described herein is defined as aprobe having such a configuration, whereby a cooling medium does notexit probe assembly 106 from a distal region of probe assembly 106. Thecooling fluid may not circulate further down the elongate shaft 184 dueto the presence of the silver solder, and flows through the coolingreturn tubes back to the cooling devices 108. In alternate embodiments,other materials may be used instead of silver solder, and the inventionis not limited in this regard. As described above, providing cooling tothe probe assemblies 106 allows heat delivered through the energydelivery devices 192 to be translated further into the tissue withoutraising the temperature of the tissue immediately adjacent the energydelivery device 192.

Referring now to FIG. 8, a cross-section of a portion of the distal tipregion 190, proximal from the cross-section of FIG. 7 as illustrated inFIG. 4, is illustrated. As shown, the secondary temperature sensingelement 404 is located proximate to an inner wall of the elongate shaft184. This proximity allows the secondary temperature sensing element 404to provide a more accurate indication of the temperature of surroundingtissue. In other words, the secondary temperature sensing element 404may be operable to measure the temperature of the inner wall of theelongate shaft 184 at the location of the secondary temperature sensingelement 404. This temperature is indicative of the temperature of tissuelocated proximate to the outer wall of the elongate shaft 184. Thus, itis beneficial to have the secondary temperature sensing element 404located proximate to an inner wall of the elongate shaft 184, ratherthan further away from the inner wall.

FIGS. 7 and 8 also illustrate the relative positions of the threehypotubes used in a first embodiment of the present invention. In thisembodiment, the three hypotubes are held together in some fashion toincrease the strength of probe assembly 106. For example, the threehypotubes may be bound together temporarily or may be more permanentlyconnected using solder, welding or any suitable adhesive means. Variousmeans of binding and connecting hypotubes are well known in the art andthe present invention is not intended to be limited in this regard.

As mentioned above, the system 100 of the present invention may furtherinclude one or more introducer tubes. Generally, introducer tubes mayinclude a proximal end, a distal end, and a longitudinal bore extendingtherebetween. Thus, the introducer tubes (when used) are operable toeasily and securely couple with the probe assembly 106. For example, theproximal end of the introducer tubes may be fitted with a connector ableto mate reversibly with handle 180 of probe assembly 106. An introducertube may be used to gain access to a treatment site within a patient'sbody and a hollow elongate shaft 184 of a probe assembly 106 may beintroduced to said treatment site through the longitudinal bore of saidintroducer tube. Introducer tubes may further include one or more depthmarkers to enable a user to determine the depth of the distal end of theintroducer tube within a patient's body. Additionally, introducer tubesmay include one or more radiopaque markers to ensure the correctplacement of the introducers when using fluoroscopic guidance.

The introducer tubes may be made of various materials, as is known inthe art and, if said material is electrically conductive, the introducertubes may be electrically insulated along all or part of their length,to prevent energy from being conducted to undesirable locations within apatient's body. In some embodiments, the elongate shaft 184 may beelectrically conductive, and an introducer may function to insulate theshaft leaving the energy delivery device 192 exposed for treatment.Further, the introducer tubes may be operable to connect to a powersource and may therefore form part of an electrical current impedancemonitor (wherein at least a portion of the introducer tube is notelectrically insulated). Different tissues may have different electricalimpedance characteristics and it is therefore possible to determinetissue type based on impedance measurements, as has been described.Thus, it would be beneficial to have a means of measuring impedance todetermine the tissue within which a device is located. In addition, thegauge of the introducer tubes may vary depending on the procedure beingperformed and/or the tissue being treated. In some embodiments, theintroducer tubes should be sufficiently sized in the radial dimension soas to accept at least one probe assembly 106. In alternativeembodiments, the elongate shaft 184 may be insulated so as not toconduct energy to portions of a patient's body that are not beingtreated.

The system may also include one or more stylets. A stylet may have abeveled tip to facilitate insertion of the one or more introducer tubesinto a patient's body. Various forms of stylets are well known in theart and the present invention is not limited to include only onespecific form. Further, as described above with respect to theintroducer tubes, the stylets may be operable to connect to a powersource and may therefore form part of an electrical current impedancemonitor. In other embodiments, one or more of the probe assemblies 106may form part of an electrical current impedance monitor. Thus, thegenerator 102 may receive impedance measurements from one or more of thestylets, the introducer tubes, and/or the probe assemblies 106 and mayperform an action, such as alerting a user to an incorrect placement ofan energy delivery device 192, based on the impedance measurements.

In one embodiment, the first and second probe assemblies 106 may beoperated in a bipolar mode. For example, FIG. 9 illustrates oneembodiment of two probe assemblies 106, wherein the distal tip regions190 thereof are located within an intervertebral disc 800. In suchembodiments, electrical energy is delivered to the first and secondprobe assemblies 106 and this energy is preferentially concentratedtherebetween through a region of tissue to be treated (i.e. an area ofthe intervertebral disc 800). The region of tissue to be treated is thusheated by the energy concentrated between first and second probeassemblies 106. In other embodiments, the first and second probeassemblies 106 may be operated in a monopolar mode, in which case anadditional grounding pad is required on the surface of a body of apatient, as is known in the art. Any combination of bipolar andmonopolar procedures may also be used. It should also be understood thatthe system may include more than two probe assemblies. For example, insome embodiments, three probe assemblies may be used and the probeassemblies may be operated in a triphasic mode, whereby the phase of thecurrent being supplied differs for each probe assembly.

In further embodiments, the system may also be configured to control oneor more of the flow of current between electrically conductivecomponents and the current density around a particular component. Forexample, a system of the present invention may include threeelectrically conductive components, including two of similar oridentical dimensions and a third of a larger dimension, sufficient toact as a dispersive electrode. Each of the electrically conductivecomponents should beneficially be operable to transmit energy between apatient's body and an power source. Thus, two of the electricallyconductive components may be probe assemblies while the thirdelectrically conductive component may function as a grounding pad ordispersive/return electrode. In one embodiment, the dispersive electrodeand a first probe assembly are connected to a same electric pole while asecond probe assembly is connected to the opposite electric pole. Insuch a configuration, electrical current may flow between the two probeassemblies or between the second probe assembly and the dispersiveelectrode. To control the current to flow preferentially to either thefirst probe assembly or the dispersive electrode, a resistance orimpedance between one or more of these conductive components (i.e. thefirst probe assembly and the dispersive electrode) and a current sink(e.g. circuit ‘ground’) may be varied. In other words, if it would bedesirable to have current flow preferentially between the second probeassembly and the dispersive electrode (as in a monopolar configuration),then the resistance or impedance between the first probe assembly andthe circuit ‘ground’ may be increased so that the current will prefer toflow through the dispersive electrode to ‘ground’ rather than throughthe first probe assembly (since electrical current preferentiallyfollows a path of least resistance). This may be useful in situationswhere it would be desirable to increase the current density around thesecond probe assembly and/or decrease the current density around thefirst probe assembly. Similarly, if it would be desirable to havecurrent flow preferentially between the second probe assembly and thefirst probe assembly (as in a bipolar configuration), then theresistance or impedance between the dispersive electrode and ‘ground’may be increased so that the current will prefer to flow through thefirst probe assembly to ‘ground’ rather than through the dispersiveelectrode. This would be desirable when a standard bipolar lesion shouldbe formed. Alternatively, it may desirable to have a certain amount ofcurrent flow between the second probe assembly and the first probeassembly with the remainder of current flowing from the second probeassembly to the dispersive electrode (a quasi-bipolar configuration).This may be accomplished by varying the impedance between at least oneof the first probe assembly and the dispersive electrode, and ‘ground’,so that more or less current will flow along a desired path. This wouldallow a user to achieve a specific, desired current density around aprobe assembly. Thus, this feature of the present invention may allow asystem to be alternated between monopolar configurations, bipolarconfigurations or quasi-bipolar configurations during a treatmentprocedure.

Referring now to FIG. 12, a flow diagram of one embodiment of a method500 for treating tissue of a patient's body, such as an intervertebraldisc 800, using the probe assemblies described herein is illustrated. Asshown at 502, the method may first include preparing the cooledradiofrequency probe assembly 106 for use to treat tissue of a patient'sbody. For example, as shown at 504, preparing the cooled radiofrequencyprobe assembly 106 to treat the tissue may include determining a desiredlesion size (or volume) and/or a rate of power delivery required totreat the tissue. Further, as shown at 506, a user may select one ormore probes 106 from a plurality of probes based on the length 414 ofthe temperature sensing element 402 thereof that achieves the desiredlesion size or the desired rate of power delivery.

Once the appropriate probe assembly(ies) 106 have been selected havingthe temperature sensing element(s) 402 of a determined length, as shownat 508, the method 500 includes positioning the probe assembly(ies) 106into the patient's body. More specifically, the method 500 may generallyinclude inserting the energy delivery device(s) 192 into the patient'sbody and routing the energy delivery device(s) 192 to the tissue of thepatient's body. For example, in one embodiment, with a patient lying ona radiolucent table, fluoroscopic guidance may be used to percutaneouslyinsert an introducer with a stylet to access the posterior of anintervertebral disc. In addition to fluoroscopy, other aids, includingbut not limited to impedance monitoring and tactile feedback, may beused to assist a user to position the introducer or probe assembly(ies)106 within the patient's body. The use of impedance monitoring has beendescribed herein, whereby a user may distinguish between tissues bymonitoring impedance as a device is inserted into the patient's body.With respect to tactile feedback, different tissues may offer differentamounts of physical resistance to an insertional force. This allows auser to distinguish between different tissues by feeling the forcerequired to insert a device through a given tissue. One method ofaccessing the disc is the extrapedicular approach in which theintroducer passes just lateral to the pedicle, but other approaches maybe used. A second introducer with a stylet may then be placedcontralateral to the first introducer in the same manner, and thestylets are removed. Thus, the probe assemblies 106 can be inserted intoeach of the two introducers placing the electrodes 192 in the tissue atsuitable distances, such as from about 1 mm to about 55 mm.

As shown at 510, the method 500 includes coupling an power source (e.g.the generator 102) to the probe assembly(ies) 106. Once in place, astimulating electrical signal may be emitted from either of theelectrodes 192 to a dispersive electrode or to the other electrode 192.This signal may be used to stimulate sensory nerves where replication ofsymptomatic pain would verify that the disc is pain-causing. Inaddition, as shown at 512, since the probe assembly(ies) 106 areconnected to the RF generator 102 as well as to peristaltic pumps 122,the method 500 includes simultaneously circulating the cooling fluidthrough the internal lumens 302, 304 via the peristaltic pumps 122 anddelivering energy from the RF generator 102 to the tissue through theenergy delivery devices 192. In other words, radiofrequency energy isdelivered to the electrodes 192 and the power is altered according tothe temperature measured by temperature sensing element 402 in the tipof the electrodes 192 such that a desired temperature is reached betweenthe distal tip regions 190 of the two probe assemblies 106.

During the procedure, a treatment protocol such as the cooling suppliedto the probe assemblies 106 and/or the power transmitted to the probeassemblies 106 may be adjusted and/or controlled to maintain a desirabletreatment area shape, size and uniformity. More specifically, as shownat 514, the method 500 includes actively controlling energy delivered tothe tissue by controlling both an amount of energy delivered through theenergy delivery devices 192 and individually controlling the flow rateof the peristaltic pumps 122. In further embodiments, the generator 102may control the energy delivered to the tissue based on the measuredtemperature measured by the temperature sensing element(s) 402 and/orimpedance sensors.

More specifically, as shown in FIG. 13, a block diagram of oneembodiment of a treatment procedure for actively controlling the energydelivered to the tissue by controlling both the amount of energydelivered through the energy delivery devices 192 and the flow rate ofthe peristaltic pumps 122 according to the present disclosure isillustrated. As shown at 600, ablation is initialized. As shown at 602,the energy dosage may be calculated using simple numerical integrationtechniques. As shown at 604, the calculated energy dosage may then becompared against a preset energy dosage threshold. If the dosage is notsatisfied as shown at 606, the procedure continues to 608 to mitigaterising impedance of the internally-cooled probe assemblies 106 duringthe treatment procedure. More specifically, as shown, one or moreprocedure parameters are monitored while delivering the energy from thegenerator 102 to the tissue through the energy delivery devices 192. Theprocedure parameter(s) described herein may include, for example, atemperature of the tissue, an impedance of the tissue, a power demand ofthe energy delivery device 192, or similar, or combinations thereof.Further, as shown, the procedure parameter(s) 608 may be fed into arising impedance detection engine 610. As shown at 612, the risingimpedance detection engine 610 is configured to determine, e.g. inreal-time, whether a rising impedance event is likely to occur in apredetermined time period (i.e. whether the rising impedance event isimminent) based on the received procedure parameter(s) 608. The risingimpedance detection engine 610 can then determine a command for the pumpassembly 120 based on whether the rising impedance event is likely tooccur in the predetermined time period.

If not imminent, as shown at 614, the cooling rate can be increased,e.g. by increasing the pump speed (e.g. via the RPM controllers 125) ofthe peristaltic pumps 122 as shown at 616. After the cooling rate isincreased, the ablation 600 continues. If a rising impedance event isimminent, as shown at 618, the cooling rate can be reduced, e.g. bydecreasing the pump speed (e.g. via the RPM controllers 125) of theperistaltic pumps 122 as shown at 620. In other words, in severalembodiments, the peristaltic pumps 122 may be independently controlledvia their respective RPM controllers 125 to alter the rate of cooling toeach electrode 192 of the probe assemblies 106. In such embodiments, thepower supply 126 of the pump assembly 120 may be decoupled, at least inpart, from the generator 102. Further, as shown, the system 550 operatesusing closed-loop feedback control 634, 636. As used herein, closed loopfeedback control refers to control whereby the generator 102 controlsthe flow rate to the probes via the peristaltic pumps 122 in order tomodulate the power to a set point independent of temperature.Alternatively, closed loop feedback may also refer to control wherebythe generator 102 controls the flow rate to the probes via theperistaltic pumps 122 in order to modulate the power to achieve desiredtotal delivered energy into the tissue.

Once the energy dosage threshold is satisfied, as shown at 622, thetreatment procedure is configured to check if the thermal dosagethreshold has been satisfied as shown at 624. If the thermal dosage hasnot been satisfied, as shown at 626, the treatment procedure proceedsthrough the independent temperature-power feedback control loop as shownat 628. More specifically, in certain embodiments, the amount of energydelivered through the energy delivery device 192 may be controlled bydefining a predetermined threshold temperature for treating the tissue,ramping up the temperature of the tissue via the generator 102 throughthe energy delivery device 192 to the predetermined thresholdtemperature, and maintaining the temperature of the tissue at thepredetermined threshold temperature to create a lesion in the tissue. Insuch embodiments, the temperature of the tissue may be maintained at thepredetermined threshold temperature as a function of at least one of apower ramp rate, an impedance level, an impedance ramp rate, and/or aratio of impedance to power.

Only when the thermal dosage threshold has been satisfied, as shown at630, the procedure terminates as shown at 632. Thus, the system andmethod of the present disclosure provides the unique features ofprobe(s) with inherently high-power demand (i.e. short thermocoupleprotrusion), a pump-modulated power algorithm, a preset energy dosage ortotal average power threshold, and/or a rising impedance detectionengine 610.

Referring now to FIG. 14, graphs of power (y-axis) versus time (x-axis)and temperature (y-axis) versus time (x-axis) for the same testprocedure are depicted to illustrate advantages of modulating powerbased on the rate of cooling. More specifically, as shown, the ablationis started with the pump assembly 120 set to its nominal speed. At timeTi into the test procedure, the cooling rate supplied to the energydelivery device 192 is decreased step-wise as shown at 650. This resultsin a decrease of the power demand as shown at 652, while the temperatureremains the same as shown at 654. As such, the control for the coolingrate operates as an independent feedback control loop from the primarytemperature-power feedback control loop (as shown at 628), the latterbeing responsible for ramping and maintaining the temperature set-pointof the tissue. Thus, the temperature set-point does not change withchanges to the cooling rate since the power required to heat the tissueis decoupled from the power required to offset the effects of thecooling.

Referring now to FIGS. 15 and 16, example graphs are depicted toillustrate various advantages of mitigating rising impedance during aninternally-cooled probe treatment procedure according to the presentdisclosure. More specifically, FIG. 15 illustrates graphs of impedance(y-axis) versus time (x-axis), temperature (y-axis) versus time(x-axis), and power (y-axis) versus time (x-axis), respectively, forthree treatment procedures that each utilize an internally-cooled probewith inherently high power demand and manual feedback control, when noimpedance mitigation is implemented. As shown at 656, the test procedureresults in high impedance errors. This results in insufficient thermaldosage and incomplete procedures as shown via the temperature 658.Further, the power demand 660 exceeds the predetermined threshold 662.

In contrast, FIG. 16 illustrates graphs of impedance (y-axis) versustime (x-axis), temperature (y-axis) versus time (x-axis), and power(y-axis) versus time (x-axis), respectively, for three treatmentprocedures that utilize an internally-cooled probe with pump-modulatedpower control. Thus, as shown, the test procedure can be fully completedwith no high impedance errors. Further, as shown, the temperatureachieves the set point. Moreover, as shown in the graph of power(y-axis) versus time (x-axis), the pump speed was slowly ramped from thelowest setting starting at the beginning of the procedure and maintainedbelow a predetermined threshold. It should be understood that thepredetermined threshold may be determined using historical testing data,or may be dynamic. In addition to controlling to a power threshold(s),other embodiments may control based on power ramp rate(s) (dP/dt),impedance level(s) (Z), impedance ramp rate(s) (dZ/dt), and/or a ratioof impedance to power. Regardless of the feedback mechanism, allembodiments are configured to determine the likelihood of a risingimpedance event and adjust the power demand accordingly by controllingthe rate of cooling to the energy delivery devices 192. For example, inseveral embodiments, the power demand of the energy delivery device maybe compared to a predetermined threshold. If the power demand is greaterthan the predetermined threshold, the rising impedance engine 610 maydecrease a speed of the pump assembly 120. If the power demand is lessthan the predetermined threshold, the rising impedance engine 610 mayincrease the speed of the pump assembly 120.

Following treatment, energy delivery and cooling may be stopped and theprobe assemblies 106 are removed from the introducers, where used. Afluid such as an antibiotic or contrast agent may be injected throughthe introducers, followed by removal of the introducers. Alternatively,the distal tips of the probe assemblies 106 may be sharp andsufficiently strong to pierce tissue so that introducers may not berequired. As mentioned above, positioning the probe assemblies 106, andmore specifically the energy delivery devices 192, within the patient'sbody, may be assisted by various means, including but not limited tofluoroscopic imaging, impedance monitoring and tactile feedback.Additionally, some embodiments of this method may include one or moresteps of inserting or removing material into a patient's body. Forexample, as has been described, a fluid may be inserted through anintroducer tube during a treatment procedure. Alternatively, a substancemay be inserted through the probe assembly 106, in embodiments whereprobe assembly 106 includes an aperture in fluid communication with apatient's body. Furthermore, material may be removed from the patient'sbody during the treatment procedure. Such material may include, forexample, damaged tissue, nuclear tissue and bodily fluids. Possibletreatment effects include, but are not limited to, coagulation of nervestructures (nociceptors or nerve fibers), ablation of collagen,biochemical alteration, upregulation of heat shock proteins, alterationof enzymes, and alteration of nutrient supply.

Referring now to FIG. 17, a graph 700 of energy (y-axis) versus lesionarea (x-axis) is provided to illustrate further advantages of thepresent disclosure. More specifically, as shown, the graph 700 providesenergy versus lesion area for three different treatment procedures.Assuming a perfectly spherical lesion volume, a predetermined desireddiameter lesion is represented by the vertical dashed line 702. A firsttest procedure 704 created a lesion using a conventional thermal dosageapproach. A second test procedure 708 created a lesion with a shorterablation time but without pump-modulated power control. A third testprocedure 706 created a lesion with a shorter ablation time andpump-modulated power control. As shown via data 708, by running theablation for a shorter time, a lesion of sufficient size cannot becreated. However, if pump-modulated power control is also implemented(as illustrated by results 706), lesions can be created on the order ofusing the conventional thermal dosage approach as represented by data704. Thus, by controlling the temperature and the energy delivery rate(i.e. by modulating the pumps 122), the energy delivery rate can bemaximized, thereby result in a much faster ablation time. In certaininstances, the ablation time can be reduced by as much as half whencompared to conventional ablation techniques.

Referring now to FIG. 18, a graph 800 depicting the high correlation 19between delivered energy (y-axis) and lesion size (x-axis) isillustrated. More specifically, as shown, the lesion width 802 isillustrated by solid dots and the lesion length 804 is represented byhollow dots. FIG. 19 illustrates a graph 850 depicting the inversecorrelation between thermocouple protrusion lengths (x-axis) and thetotal delivered energy (y-axis). In addition, FIG. 20 illustrates agraph 900 depicting the correlation between lesion size (y-axis) andthermocouple protrusion distance (x-axis). Taken together, FIGS. 18-20demonstrate the effects that the thermocouple protrusion length ordistance can have on the generated lesion size through controlling theamount of delivered energy into the tissue. More specifically,thermocouple protrusion length and lesion size are inversely correlated.As such, this characteristic can be exploited to generate various lesionsizes targeting different anatomical locations.

A system of the present invention may be used in various medicalprocedures where usage of an energy delivery device may provebeneficial. Specifically, the system of the present invention isparticularly useful for procedures involving treatment of back pain,including but not limited to treatments of tumors, intervertebral discs,facet joint denervation, sacroiliac joint lesioning or intraosseous(within the bone) treatment procedures. Moreover, the system isparticularly useful to strengthen the annulus fibrosus, shrink annularfissures and impede them from progressing, cauterize granulation tissuein annular fissures, and denature pain-causing enzymes in nucleuspulposus tissue that has migrated to annular fissures. Additionally, thesystem may be operated to treat a herniated or internally disrupted discwith a minimally invasive technique that delivers sufficient energy tothe annulus fibrosus to breakdown or cause a change in function ofselective nerve structures in the intervertebral disc, modify collagenfibrils with predictable accuracy, treat endplates of a disc, andaccurately reduce the volume of intervertebral disc tissue. The systemis also useful to coagulate blood vessels and increase the production ofheat shock proteins.

Using liquid-cooled probe assemblies 106 with an appropriate feedbackcontrol system as described herein also contributes to the uniformity ofthe treatment. The cooling distal tip regions 190 of the probeassemblies 106 helps to prevent excessively high temperatures in theseregions which may lead to tissue adhering to the probe assemblies 106 aswell as an increase in the impedance of tissue surrounding the distaltip regions 190 of the probe assemblies 106. Thus, by cooling the distaltip regions 190 of the probe assemblies 106, higher power can bedelivered to tissue with a minimal risk of tissue charring at orimmediately surrounding the distal tip regions 190. Delivering higherpower to energy delivery devices 192 allows tissue further away from theenergy delivery devices 192 to reach a temperature high enough to createa lesion and thus the lesion will not be limited to a region of tissueimmediately surrounding the energy delivery devices 192 but will ratherextend preferentially from a distal tip region 190 of one probe assembly106 to the other.

As has been mentioned, a system of the present invention may be used toproduce a relatively uniform lesion substantially between two probeassemblies 106 when operated in a bipolar mode. Oftentimes, uniformlesions may be contraindicated, such as in a case where a tissue to betreated is located closer to one energy delivery device 192 than to theother. In cases where a uniform lesion may be undesirable, using two ormore cooled probe assemblies 106 in combination with a suitable feedbackand control system may allow for the creation of lesions of varying sizeand shape. For example, preset temperature and/or power profiles thatthe procedure should follow may be programmed into the generator 102prior to commencement of a treatment procedure. These profiles maydefine parameters (these parameters would depend on certain tissueparameters, such as heat capacity, etc.) that should be used to create alesion of a specific size and shape. These parameters may include, butare not limited to, maximum allowable temperature, ramp rate (i.e. howquickly the temperature is raised) and the rate of cooling flow, foreach individual probe. Based on temperature or impedance measurementsperformed during the procedure, various parameters, such as power orcooling, may be modulated, to comply with the preset profiles, resultingin a lesion with the desired dimensions.

Similarly, it is to be understood that a uniform lesion can be created,using a system of the present invention, using many different pre-settemperature and/or power profiles which allow the thermal dose acrossthe tissue to be as uniform as possible, and that the present inventionis not limited in this regard.

It should be noted that the term radiopaque marker as used hereindenotes any addition or reduction of material that increases or reducesthe radiopacity of the device. Furthermore, the terms probe assembly,introducer, stylet etc. are not intended to be limiting and denote anymedical and surgical tools that can be used to perform similar functionsto those described. In addition, the invention is not limited to be usedin the clinical applications disclosed herein, and other medical andsurgical procedures wherein a device of the present invention would beuseful are included within the scope of the present invention.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A method for preparing a cooled radiofrequency probe for use to treattissue of a patient's body, the method comprising: providing a pluralityof cooled radiofrequency probes, each of the plurality of cooledradiofrequency probes comprising an elongate member with a distal regionand a proximal region, the distal regions each having an electricallyand thermally-conductive energy delivery device for delivering one ofelectrical and radiofrequency energy to the patient's body, theelectrically and thermally-conductive energy delivery devices eachhaving one or more internal lumens for circulating a cooling fluidtherethrough and an electrically and thermally-conductive protrusionhaving a temperature sensing element, the temperature sensing elementseach extending from a distal end of the energy delivery device, each ofthe temperature sensing elements comprising a different length thatextends from the distal end of the energy delivery device; determining,via a power source, at least one of a desired lesion size or a desiredrate of power delivery required to treat the tissue; and selecting oneof the probes from the plurality of cooled radiofrequency probes basedon the length of the temperature sensing element thereof that achievesthe desired lesion size or the desired rate of power delivery.
 2. Themethod of claim 1, wherein an actual lesion size varies with thedifferent lengths of the temperature sensing elements.
 3. The method ofclaim 2, wherein temperature sensing elements comprising longer lengthsgenerate lesions of smaller sizes and temperature sensing elementscomprising shorter lengths generate lesions of larger sizes.
 4. Themethod of claim 1, wherein the different lengths of the temperaturesensing elements are less than about 1 millimeter (mm).
 5. The method ofclaim 4, wherein the different lengths of the temperature sensingelements range from about 0.20 mm to about 0.70 mm.
 6. The method ofclaim 1, wherein the desired lesion size or the desired rate of powerdelivery is based on a treatment procedure type of the tissue.
 7. Themethod of claim 1, further comprising measuring the temperature of thetissue using the selected temperature sensing element.
 8. The method ofclaim 1, wherein each of the temperature sensing elements has adifferent shape.
 9. The method of claim 1, further comprising decouplinga temperature control of the temperature sensing element from the powersource within a certain operating envelope by controlling the coolingmedium flow rate in a closed loop manner.
 10. A system for treatingtissue of a patient's body, the system comprising: a power source; and aplurality of cooled radiofrequency probes communicatively coupled to thepower source, each of the probes comprising an elongate member with adistal region and a proximal region, the distal regions having anelectrically and thermally-conductive energy delivery device fordelivering one of electrical and radiofrequency energy to the patient'sbody, the electrically and thermally-conductive energy delivery deviceshaving one or more internal lumens for circulating a cooling fluidtherethrough and an electrically and thermally-conductive protrusionhaving a temperature sensing element, each of the temperature sensingelements extending from a distal end of the energy delivery device, eachof the temperature sensing elements of each of the probes comprising adifferent length that extends from the distal end of the energy deliverydevice, wherein a user can select one of the probes from the pluralityof cooled radiofrequency probes based on the length of the temperaturesensing element thereof that achieves a desired lesion size or a desiredrate of power delivery.
 11. The system of claim 10, wherein the lesionsize varies with the different lengths of the temperature sensingelements.
 12. The system of claim 11, wherein temperature sensingelements comprising longer lengths generate lesions of smaller sizes andtemperature sensing elements comprising shorter lengths generate lesionsof larger sizes.
 13. The system of claim 10, 11, or 12, wherein thedifferent lengths of the temperature sensing elements are less thanabout 1 millimeter (mm).
 14. The system of claim 13, wherein thedifferent lengths of the temperature sensing elements range from about0.20 mm to about 0.70 mm.
 15. The system of claim 10, wherein thedesired lesion size or the desired rate of power delivery is based on atreatment procedure type of the tissue.
 16. A method of treating tissueof a patient's body, the method comprising: providing a plurality ofcooled radiofrequency probes, each of the plurality of cooledradiofrequency probes comprising an elongate member with a distal regionand a proximal region, the distal regions each having an electricallyand thermally-conductive energy delivery device for delivering one ofelectrical and radiofrequency energy to the patient's body, theelectrically and thermally-conductive energy delivery devices eachhaving one or more internal lumens for circulating a cooling fluidtherethrough and an electrically and thermally-conductive protrusionhaving a temperature sensing element, the temperature sensing elementseach extending from a distal end of the energy delivery device, each ofthe temperature sensing elements comprising a different length thatextends from the distal end of the energy delivery device; determiningat least one of a desired lesion size or a desired rate of powerdelivery required to treat the tissue; selecting one of the probes fromthe plurality of cooled radiofrequency probes based on the length of thetemperature sensing element thereof that achieves the desired lesionsize or the desired rate of power delivery; inserting the selected probeinto the patient's body; routing the selected probe to the tissue of thepatient's body; and simultaneously circulating the cooling fluid throughthe one or more internal lumens via at least one pump assembly anddelivering energy from the power source to the tissue through the energydelivery device.
 17. The method of claim 16, wherein temperature sensingelements comprising longer lengths generate lesions of smaller sizes andtemperature sensing elements comprising shorter lengths generate lesionsof larger sizes.
 18. The method of claim 16, wherein the differentlengths of the temperature sensing elements are less than about 1millimeter (mm).
 19. The method of claim 16, wherein the desired lesionsize or the desired rate of power delivery is based on a treatmentprocedure type of the tissue.
 20. The method of claim 16, wherein eachof the temperature sensing elements have a different shape.